Vibrationless percussive tool



April 10, 1962 c. LEAVELL VIBRATIONLESS PERCUSSIVE TOOL 2 Sheets-Sheet 1Filed June l5, 1960 C. LEAVELL 2 Sheets-Sheet 2 Filed June 15, 1960United States Patent Ohice 3,028,840 Patented Apr. 10, 1962 3,023,840VllBATiONLlESS PERCUSSWE TOL @harias Leni/eli, 266 S. Fairfield Ava,Lombard, lll. Filed .lune 15, 196i), Ser. No. 36,301 Claims. (Cl.121-13) This invention relates to gas-actuated percussive tools as, forexample, pneumatic paving breakers, and is particularly concerned withimproving such tools by making the operation thereof substantiallyvibrationless.

Considering the paving breaker as an exemplication of environments inwhich the invention has utility, the structural composition thereofincludes a casing defining an axially extending cylinder therein, ahammer or piston reeiprocable within the cylinder, and a steel spike orwork member slidably carried by the casing for limited axial movementwith respect thereto and which is adapted to receive impact from thehammer (usually thro-ugh an anvil or tappet interposed therebetween) atone end of the reciprocatory stroke thereof. The impact transmitted bythe hammer to the spike is delivered thereby to a concrete slab or otherwork material to break or demolish the same, and the hammer isreciprocated within its cylinder by the alternate application ofpressure fluid to the opposite ends thereof.

In the usual paving breaker, the charges of compressed air alternatelyadmitted into the opposite ends of the cylinder to respectivelyreciprocate the hammer in directions toward and away from the spike areeach reactively applied against transverse surfaces defining the endclosures of the cylinder, and as a consequence the casing is moved orvibrated in opposite directions along the axis of reciprocation of thehammer. In many tool structures, the hammer is reciprocated throughapproximately 1,20) cycles each minute, and consequently, the pressureforces reacting alternately against opposite ends of the casing cylinderintroduce a violent and objectionable vibration into the casing. Thus,in the usual paving breaker, the compressed air pressure force reactingalternately against opposite ends of the casing cylinder deiinesconnecting structure accomplishing a necessary transmission of forcebetween the hammer which is a desirably or unavoidably vibrating bodyand the casing which Vis a body in which the occurrence of vibration isobjectionable.

rl`he present invention is concerned with eliminating vibrationordinarily introduced into the casing of such a percussive tool by thepressure forces reactively applied to the casing cylinder in actuatingthe hammer by counterbalancing such reactive forces with thesimultaneous application to the casing of substantially equal andopposite pressure forces. balancing system includes a hermetic barrierthat, in the specific structure considered in detail herein, takes theform of an oscillator or oscillatory mass member that reciprocateswithin a cylinder therefor; and it has been found that in certainsituations, random and irregular recoil forces are fed into the toolstructure through the steel spike as a result of the non-homogenity ofthe slab being penetrated thereby, and such recoil forces tend to causethe oscillator to migrate toward one end of its cylinder and to impactthe end closure thereof which is an undesirable condition since it wouldreintroduce vibration into the casing. Therefore, the present inventionis also concerned with avoiding such a condition of impact relationbetween the oscillator and end of its cylinder, and does so bystablizing the mean position of the oscillator with an automatic controlsystem that includes a pneumatic column operative between the oscillatorstructure and one end of its cylinder, which pneumatic column denes aforce-transmitting linkage structure coupling the necessarily vibratingoscillator and cylinder therefor Such pressure-force counterin which thepresence of vibration is objectionable, that also includes anarrangement for maintaining the force defined by such pneumatic-columnrelatively constant during any one cycle of reciprocation of theoscillator, and that further includes pneumatic feedback means forregulatively adjusting the value of such relatively constant forceduring a plurality of reciprocations of the oscillator to positionallystabilize the same as aforesaid in order to maintain it in a conditionof intermediacy relative to the ends of its cylinder.

Embodiments of the invention are illustrated in the accompanyingdrawings, in which- FGURE l is a vertical sectional view of a pneumaticpercussive tool embodying the invention; FIGURE 2 is an enlarged, brokenvertical sectional view of a portion of the tool illustrated in FIGUREl; FIGURE 3 is a partial vertical sectional view of a modified pneumaticpercussive tool embodying the invention; FIGURE 4 is a side view inelevation of the tool shown in FIGURE 3, and in which portions thereofare broken away and are illustrated in section; and FIGURE 5 is atransverse sectional view taken along the line 5-5 of FIGURE 3.

The tool structure illustrated in FIGURE 1 is a pneumatically-actuatedpaving breaker, and to a great extent embodies a conventional vibratorytool. Thus, the structure comprises a casing 11 providing a maincylinder 12 having therein a pneumatically-actuated free-piston hammeror mass member 13. The casing 11 is equipped with handles T, andprovides an exhaust port or passage 14 to atmosphere communicating withthe cylinder 12 intermediate the ends thereof. The upper end of thecylinder 12 is occupied by a conventional valve composition operative todirect the ow of gaseous iiuid (such as compressed air) alternately tothe lower and upper end portions of the cylinder to energize thereciprocatory cycle of the hammer 13 by selectively applying upwardlyand downwardly active axial pressure forces alternately to the lowersurface 13a and to the upper surface 13b thereof.

The bottom cylinder head area facing the lower surface 13a of the hammerconsists only of the upwardly facing surface of the annular shoulderdefined around and having a sliding relation with the upper end portionof the anvil element 15. The top cylinder head area facing the surface13b of the hammer is made up of the downwardly facing surfaces of thevalve composition occupying the upper end of the cylinder. Foridentication, the annular bottom and aggregate top cylinder head surfaceareas are respectively denoted with the numbers 12a and 12b.

The anvil 15 has an enlarged seal-equipped intermediate portion 15a thatreciprocates within an anvil chamber 16, and the anvil chamber has lowerand upper end closures 16a and 16b whichy respectively engage Vthe lowerand upper stems of the anvil in sealing relation therewith, the latterof which extends into the cylinder 12 and has an upper surface 15badapted to be struck by the hammer 13. The lower end portion of theanvil chamber, 16 adjacent the closure 16a thereof is connected with thelower end o'f the cylinder 12 by a passage 17, and there.- fore thelower end portions of the anvil chamber and cylinder are pressurizedsimultaneously.y

The upper end portion of the anvil chamber 16 adjacent the end closure161; thereof is exhausted to atmosphere through a passage 18, and thelower end portion of the anvil which extends through the surface 16a andis sealingly related therewith is adapted to rest upon the upper innerend of a steel spike or work member 19 slidably carried by the casing 11for limited axial movement with respect thereto. Ordinarily, the spike19 will have a pointed lower end, and may be equipped intermediate theends thereof with an outwardly projecting annular t flange cooperativewith the usual retainer element carried by the casing for removablyconstraining the spike within the casing.

In operation of the structural arrangement thus far described, andassuming initially a parts configuration in which the hammer 13 is inabutment with the upper surface 15b of the anvil, a charge of compressedair will be directed by the valve composition into the lower end portionof the cylinder 12 through a passage 17a in the tool casing. Such chargeof air acting upwardly upon the bottom surface 13a of the hammer willreciprocate the hammer upwardly through the return stroke thereo-f.Simultaneously, however, a reactive pressure force acting downwardlyupon the lower reaction surface (the terms lower reaction surface andupper reaction surface respectively designating the total upwardlyfacing and total downwardly facing surface areas reactively pressurizedby the charges of air reciprocating the hammer, and which respectivelytransmit downwardly directed and upwardly directed axial forces to thecasing; and which in the subject structure respectively comprise theaforesaid surfaces 12a and 16a, and the aforesaid surface 12b) willcause the casing 11 to vibrate downwardly as the hammer 13 isreciprocated through its return stroke, and such reactive pressure forceis applied to the casing until the upwardly moving hammer passes theexhaust port 14, at which time the lower end portion of the cylinder 12as well as the lower end portion of the anvil chamber 16 will beexhausted to atmosphere.

As the hammer 13 approaches the upper end closure of the cylinder 12,the valve composition directs a charge of compressed air into the upperend portion of the cylinder, and the resulting pressure force actingdownwardly upon the hammer reciprocates it into impact with the surface15b of the anvil which delivers such impact to the spike 19.Simultaneously, however, such charge of compressed air exerts anupwardly directed reactive force against the upper reaction surface ofthe casing or of the cylinder defined thereby which vibrates the casingupwardly, and such reaction force is applied to the casing until thedownwardly moving hammer 13 passes the exhaust port 14, at which timethe upper end portion of the cylinder 12 is exhausted to atmosphere.

Since the reciprocatory frequency of the hammer in a conventionalvibratory tool may approach and exceed 1,200 cycles per minute, thecasing thereof would objectionably vibrate longitudinally at the samerapid rate; but with reference to the present invention, the aforementioned counterbalancing system is effective to nullify such reactivepressure forces that normally cause such casing vibration; and thestructural arrangement accomplishing this counterbalancing in the toolof FIGURE 1 will now be described.

Operative externally of the main tool casing 11 is an oscillator 20which is reciprocable in its own cylinder or support structure 21secured to the main tool casing so as to be rigidly related thereto.This oscillator element comprises a massive body or piston portion 20ahaving upper and lower stems 20b and 20c extending coaxially from theupper and lower surfaces of such piston portion. These surfaces formannular shoulders or piston surfaces 20d and 20e, and are reciprocablerelative to and in coaxial relation with the respectively opposingannular cylinder head surfaces 21a and 2lb carried by the casing(respectively denoted hereinafter as upper and lower counterbalancingsurfaces).

It will be observed in the drawings that the oscillator cylinder 21, andmore particularly the variable-volume annular space 21c thereof definedbetween the upper piston and cylinder head surfaces 20d and 21a,connects by a tube or passageway 17b and the longitudinal passageway 17ato the variable-volume space under the hammer 13 in the main cylinder12. Similarly, the lower variable-volume space 21d in the oscillatorcylinder and the variable-volume space above the hammer 13 in the maincylinder 12 are connected by a tube or passageway 22.

Before describing the operation of the tool with reference to thepressure-force counterbalancing system, it should be noted that theaxially projected areas of the upper reaction surface 12b in the maincylinder 12 and the lower counterbalancing surface 2lb in the oscillatorcylinder 21 are substantially equal, and similarly, that the axiallyprojected areas of the lower reaction surface 12a plus 16a in the maincylinder 12 and the upper counterbalancing surface 21a of the oscillatorcylinder 21 are substantially equal, for such conditions of equalityprovide the most ideal functioning of lthe pressure-forcecounterbalancing system. In the specific tool structure considered, anadditional equality is present in that the axially projected areas ofthe lower and upper surfaces 13a and 13h of the hammer are substantiallyequal, and approximately equal thereto are the axially projected areasof the lower and upper reaction surfaces.

Considering again the operation of the tool, and assuming the sameinitial condition thereof, the admission of a charge of compressed airbeneath the hammer to reciprocate the same upwardly, and whichnecessarily applies a downwardly directed reactive pressure forceagainst the casing, will simultaneously apply an upwardly directedpressure force against the casing or, more specifically, against theupper counterbalancing surface 21a thereof, because of theinterconnection of the upper end portion 21e of the oscillator cylinderwith the lower end of the cylinder 12 through the conduit 17b andpassage 17a. Since the axially projected areas of the uppercounterbalancing surface 21a and the lower reaction surface areapproximately equal, the upwardly and downwardly directed pressureforces applied simultaneously to the casing are substantially equal and,therefore, counterbalance and effectively eliminate downward vibratorymovement of the casing which would otherwise result from the admissionof compressed air into the lower end portion of the cylinder 12 toreciprocate the hammer 13 upwardly.

Correspondingly, when a charge of air is introduced into the upper endportion of the cylinder 12 to reciprocate the hammer 13 downwardly, thereactive force acting against the upper reaction surface of the casingand which tends to vibrate the same upwardly is counterbalanced by thesimultaneous application of a downwardly directed pressure force uponthe casing or, more specifically, against the lower counterbalancingsurface 2lb because of the interconnection of the lower end portion 21dof the oscillator cylinder with the upper end portion of the cylinder'12 through the tube 22. Since the axially projected areas of the upperreaction surface of the cylinder 12 and the lower counterbalancingsurface 2lb of the oscillator are substantially equal, the reactivepressure force which would otherwise vibrate the casing 11 upwardly iseffectively counterbalanced.

It will be noted in the tool of FIGURE l that the oscillator compositionis attached as a unit to the casing 11 of a conventional paving breaker,and this implies the use of such composition as an accessory forordinary vibratory type paving breakers for the purpose of convertingsuch tools for vibrationless performance. Such attachment cannot bepractically achieved by placing the type of oscillator structure shownabove the handle and backhead element of the tool, for such positioningwould increase the length of the tool to the point that an operatorcould not lean over it conveniently to apply downpush thereto, andtherefore the oscillator structure is best applied alongside of thecasing.

However, if in such placement the reciprocatory axes of the hammer 13and oscillator 20 are made parallel, the necessary displacementtherebetween denes a laterally extending or radial lever arm equal inlength to the distance between the axes and operative relative to thefulcrum or pivot structure established by the seating of the spike pointin the pit made thereby in the stationary concrete slab. As aconsequence, the tool will tend to vibrate angularly about such fulcrum.This tendency toward angular vibration is eliminated by orienting theosu cillator and hammer axes as shown in FIGURE l, which reduces suchlever arm to an eiective length of zero by providing that both thehammer and oscillator axes contain the fulcrum or pivot deiined by thespike point. This condition may be termed the copivotal relation of theham mer and oscillator axes, and the excellence of the results obtaineddepends upon the limitation of the copivotal angle (that is, the angledefined between the hammer and oscillator axes) to a sufficiently smallvalue so that the cosine thereof approximates unity.

It will be apparent that the counterbalancing action requires phases ofoperation during which each of the surfaces Zia and 21h is pressurizedwithout the other of these surfaces being simultaneously pressurized;and in terms of structure, this requirement defines the condition thatthe oscillator 2d be a hermetic barrier interposed between the surfacesZia and 2lb to maintain pneumatic isolation therebetween. It is furtherevident that the oscillator in this environment is necessarily subjectedto reversing forces of a substantial order of magnitude, and must besupported 'Within its cylinder with a positional ability such that it ismaintained intermediate the ends of the cylinder in a non-impactingrelation therewith so as not to transmit any uncounterbalanced variableforces to the casing. The structural arrangement for accomplishing thiscondition of positional stability includes a piston 26 extendingupwardly from the top of the stern Ziib of the oscillator. A cylinder Z4that slidably receives piston 2,3 is provided with escape holes 25apermitting the cylinder to exhaust to atmosphere, and the uncapped upperend 24a of the cylinder opens into an annular tank 26 dening a constantpressure space 27 therein. The space below the bottom surface of thepiston 23 is maintained at atmospheric pressure through the agency ofports 2S.

The escape holes 25a lead into an annular space 25b deiined around thecylinder 24, and the escaping air collected in this annular space isexhausted to atmosphere through a spring biased valve 25e. This valveand annular space are optional and function to prevent the pressure inthe cylinder 2d and constant pressure space 27 from dropping below arelatively low predetermined value (for example, 3 pounds per squareinch gauge) suicient to hold the oscillator 2G in its downmost positionwhen the tool is not running, and prevents the first upward oscillationsof the oscillator from carrying it into impact with its own uppercylinder head Zita. As seen in FIGURE 2, a restricted orifice 29 isprovided in a plate extending transversely across the infeed line Si),and supplies air to the aforesaid constant pressure space 27. The escapeholes 25a, collection space 25h and valve 25C together comprise theexhaust system for the space 27, and for convenience such system in itsentirety is designated with the numeral 25. This exhaust system 25together with the restricted infeed orifice 29 and piston 23 actingcooperatively therewith in a manner described hereinafter, comprise theaforementioned automatic control system whereby the aforesaid conditionof positional stability is imposed upon the oscillator 2t).

This composite automatic control system is pneumatically energized by ahigh pressure inflow through the restricted orifice i219, whichgenerally effects a substantial pressure drop, and into and through thecomposite space consisting of the constant pressure space 27 and spacein the upper portion of the cylinder 24, to commence its escapetherefrom to atmosphere, whenever the position of the piston seal 23apermits, through the small ports 25a which collectively comprise aconsiderably greater cross-sectional area than that of the inow oriiice29. It may be noted that the cylinder 24 need not necessarily have anopen upper end as shown, which is the ideal condition, but any lesseropening connecting the cylinder and constant pressure space 27 should besuiiiciently large so that substantially no pressure gradients willdevelop in the reciprocating air ilow between the upper end portion ofthe cylinder and the constant pressure space.

The composite automatic control system is utilized to keep theoscillator from striking the cylinder heads 21a and 2lb, and theprincipal tendency of the oscillator in this respect is to rise duringits oscillatory motion toward a condition of impact with the uppercylinder head v21a-- which may be explained in terms of the forcesacting on the hammer i3 as follows: First, the only forces actingdownwardly upon the hammer are the intermittently effective pneumaticforces (omitting the force of gravity which is negligible andineffective when the tool is operated in a horizontal position).Secondly, intermittently effective pneumatic forces act upwardly uponthe hammer, but in addition there is a mechanical force which assistssuch upwardly acting pneumatic forces in urging the harnmer upwardly.Such mechanical force is caused by the impact relation of the hammer andanvil for when the hammer strikes the anvil, the anvil is urgeddownwardly for an extremely brief interval by an extremely large forcewhich may approach a value of 50,900 pounds. Action and reaction beingequal, the hammer is urged .upwardly by this very large force.

must be less than the average value of the pneumatic forces actingdownwardly thereon inasmuch as the mean position of the hammertremainsfairly lixed during operation of the tool; for, since `the hammer doesnot migrate beyond the limits of its cylinder during operation of thetool, it is necessarily implied that the respective average values ofall of the forces acting downwardly on the hammer and of all of theforces acting upwardly thereagainst are very closely equal; whence, morespecically, the average value of the total pneumatic and mechanicalforce acting upwardly upon the hammer must be almost exactly equal tothe average value of the pneumatic force acting downwardly thereagainst;so that it follows that the average value of the pneumatic forces actingupwardly against the hammer must. be substantially less than the averagevalue of the pneumatic forces acting downwardly thereon,

Since the space 21C above the oscillator is in open communication withthe space in the cylinder l2 below the hammer, and the space 2id belowthe oscillatoris in open communication with the space in the cylinderab-ove the hammer, the average values of the pressures in theseoscillator spaces are substantially equal respectively to the averagevalues of the pressures in the cylinder spaces below and above thehammer. Therefore, in 'consequence of the foregoing argument, there isan effective preponderance of the average value of the pneumatic forceacting imposes upon the oscillator a continuous tendency Ito rise which,if not arrested, would reintroduce vibration into the casing lll sincethe oscillator would pound against the upper cylinder head surface 21a.c

To prevent this, an additional surface is employed on the oscillatoragainst which suicient pressure can be developed to hold the oscillatordown whereby it can be made to operate over a reciprocatory rangeintermediate the ends of its maximum stroke so that it will not strikethe cylinder heads 21a and 2lb respectively above and below theoscillator, and such additional surface is the top surface of the piston23 in the automatic control system comprising the previously specifiedelements 29, 25a, Zb, 25e and 23a, together with the piston 23 and thecontinuous space within the tank 26 and cylinder Z4.

This composite structure operates so that if the oscillator 2li startsto oscillate about a mean position which is too high, thereby causing adanger of impact with the cylinder head 21a, the piston 23 will riseupwardly with sa? the oscillator and will close the escape holes 25a, asseen best in FIGURE 2. The establishment of this condition preventsescape of air from the total space above the piston 23, and thecompressed air continuously fed into this space through the restrictedinlet orice 29 will cause the pressure therein to increase in value and,as a consequence, the oscillator will be urged downwardly with asteadily increasing pressure force until it reaches a position in whichthe escape holes a are uncovered during at least part of thereciprocatory cycle of the oscillator. If the oscillator is forceddownwardly until the escape holes remain uncovered during the entirereciprocatory cycle of the oscillator, the pressure within the spaceabove the piston 23 will drop rapidly. The pressure will then continueto decrease until it no longer gives sufficient assistance to thepressure force acting on the surface 20d of the oscillator to hold it insuch lower position, and the oscillator will then start to rise towardits stable intermediate location in which the escape holes are coveredduring a part of each cycle of reciprocation.

Experience has shown that migration of the oscillator such that theescape holes are either closed or open during the entire reciprocatorycycle of the oscillator is held to brief durations, and there istherefore a strong tendency for the oscillator to remain stabilized inan intermediate location wherein the escape holes are closed during onlya part of each reciprocatory cycle of the oscillator. It should beunderstood that sucessful operation of the automatic control in thispartciular structural design requires compensatory changes in thepressure acting downwardly on the surface of the piston 23 to beeffected quickly since the average value of the mechanical impact forcereactively delivered during any relatively short interval by the anvil14 upwardly against the bottom of the hammer 13 is related to thestrength and elastic properties of the concrete being encountered by thespike 19 during that same intervaLVand such qualities of the concreteare subject to rapid variations. It will be apparent that the purpose ofthe relatively large pressurized space comprising the space 27 and spacewithin the cylinder 24 in communication therewith, as compared to thecyclic displacements of the piston 23, is to assure that the value ofthe force present in the force-transmitting linkage detined by the aircolumn connecting the casing structure and oscillator will remainsubstantially constant during each cyclic displacement of the oscillatorso as to invest such force-transmitting linkage with the valuableincapacity to transmit vibration between two bodies necessarilyinterconnected thereby, being respectively an unavoidably vibratingbody-namely, the oscillator 2 r and a body in which the occurrence ofvibration is objectionable-namely, the oscillator cylinder `and otherelements of the composite casing structure.

A modified form of tool embodying the invention is illustrated inFIGURES 3 through 5, which both stnlcturally and functionally issubstantially the same as the tool heretofore described except that theoscillator and directly associated components have been divided into twoseparate but identical systems to effect an over-all compactness of thetool structure. Thus, instead of a single oscillator 20, a plurality(namely, two oscillatory masses) are incorporated in the structure.

To facilitate appreciation of the correspondence of parts in the twotool structures, the same numerals are employed to identify suchcorresponding parts except that in the drawing illustrating the modifiedconstruction each of the reference numerals is in the 100 series. Thus,the tool has a handle-equipped casing 111 provided with a main cylinder112 having a hammer 113 reciprocable therein for impact engagement withthe upper surface 115b of an anvil 11S that engages the upper inner endof a spike 119 slidably held by the casing for limited axial movementwith respect thereto. The hammer has and upper pressurizable surface113:1 and a lower pressurizable surface 113b, and the axially projectedareas thereof are substantially equal. The lower closure of the cylinderwhich sealingly surrounds the upper end portion of the anvil is denotedwith the numeral 112a and this surface, along with the surface 115@defining the lower end closure of the anvil chamber 116, comprise thelower reaction surface of the tool. The cylinder also has an upper endclosure (not shown) comprised mainly of the control valve that definesthe upper reaction surface of the tool. The axially projected areas ofthe lower reaction surface and upper reaction surface are substantiallyequal, respectively, to the axially projected areas of the pressurizablei ammer surfaces 113b and 113a.

Provided by the casing 111 are a pair of oscillator cylinders 121, eachof which has an oscillatory mass member supported therein forreciprocable movement. Each oscillator has an upper pressurizablesurface 12%, and corresponding thereto the upper end portion 121C of theassociated oscillator cylinder has an end closure 121a. The aggregatesurfaces 121a (one such surface being provided by each oscillatorcylinder) comprise the upper counterbalancing surface of the toolstructure, and the total or sum of the axially projected areas of thesetwo surfaces-ie., the area of the upper counterybalancing surface issubstantially equal to the axially projected area of the lower reactionsurface of the tool. Each of the oscillator cylinder spaces 121e isconnected with the lower end portion of the main cylinder 112 throughthe passage network 117b and 117er. Each of the oscillatory masses 120has a lower pressurizable surface 120e, and in facing relation therewithare the respective lower cylinder end closures 121b. The sum of theaxially pro jected areas of the surfaces 12111 which together comprisethe lower counterbaiancing surface of the tool structure s substantiallyequal to the axially projected area of the r upper reaction surface ofthe tool. The lower end portion 12M of each oscillator cylinder isconnected to the upper end portion of the main cylinder 112 through therespective passages 122.

Corresponding to the structural components illustrated particularly inFIGURE 2 but inverted in orientation, each of the oscillators 120 isequipped with a downwardly extending stem 120b which carries a piston123 adjacent the lower end thereof. The stem of each oscillatorsealingly extends through the cylinder end closure 121b associatedtherewith, and each of the pistons is reciprocable within a cylinder 124therefor. The lower end portion of each cylinder 124 is exhausted toatmosphere through a plurality of ports 128, and the upper end portionof each such cylinder is connected through a port and passage system124a with a plurality of constant pressure spaces or chambers 127defined by the casing parts 126 (FIGURE 5). Each of the pistons 123reciprocates about exhaust or escape holes 125a which communicatedirectly with atmosphere, in contrast to the embodiment of FGURES 1 and2 wherein the corresponding holes 25a are connected with atmospherethrough a collection chamber and spring biased valve. It will beunderstood that the constant pressure spaces 127 are connected to asource of compressed air through suitable passages and pressure reducingrestrictions as in the prior embodiment-such source of compressed airbeing the actuating supply air delivered to the tool through the inletcoupling 110.

It will be evident from the foregoing description of the tool structureillustrated in FIGURES 3 through 5 that the operation thereof issubstantially the same as that of the tool embodiment shown in FIGURES 1and 2. Therefore, the briefest operational summary will sufce, and itneed only be said that the reactive force acting downwardly on the lowerreaction surface and tending to vibrate the tool casing downwardly whenthe hammer is reciprocated upwardly through its return stroke iscounterbalanced by the substantially equal and oppositely directedcounterbalancing force resulting from the pressure forces in theoscillator cylinder spaces 121e acting upwardly on the uppercounterbalancing surface of the tool structure. Similarly, the upwardlydirected pressure force reactively applied to the upper reaction surfaceof the casing when the hammer is reciprocated downwardly iscounterbalanced by the oppositely directed pressure forces in theoscillator cylinder spaces 121:1 acting downwardly on the lowercountcrbalancing surface of the tool structure.

The composite automatic control system comprising the two controlsystems respectively associated with the two oscillators 120 maintainsthe same in positions of non-impacting intermediacy between the ends oftheir respectively associated cylinders f2.1, and thevibrationeliminating constant pressure columns respectively actdownwardly upon the two pistons T123 and are regulatively adjusted invalue to enforce such positional stability upon the oscillator asdescribed in connection with the r'irst embodiment of the invention. itmay be noted that the reciprocatary axes of the oscillatory mass members120 are coplanar with and symmetrically related to (in the illustratedstructure, parallel to) the axis of reciprocation of the hammer M3, and,therefore, that the center of gravity of the total oscillator mass iscoincident with that of the hammer so that no angular or torsionalvibration is introduced into the tool by the reciprocatory motions ofthe oscillators.

The present invention constitutes a continuation-in-part of my copendingpatent application, Serial No. 742,878, filed `Tune 18, 1958.

While iu the foregoing specification embodiments of the invention havebeen described in considerable detail for purposes of making a completedisclosure, it will be apparent to those skilled in the art thatnumerous changes may be made in those details without departing from theprinciples or spirit of the invention.

I claim:

l. in a percussive tool, an outer casing structure, a rst lmass memberreciprocable with respect to said outer casing structure, means linkingsaid first mass member and said casing structure for the transmission ofa reversing force therebetween energizing reciprocation of said firstmass member relative to said casing structure for delivering impactforce to a work element, a pair of mass members reciprocable withrespect to said casing structure, means linking said pair of massmembers and said casing structure for the transmission of a reversingforce therebetween energizing reciprocation of said pair of mass membersrelative to said casing structure in force opposition to thereciprocatory movement of said first mass member, and a pair of meansfor respectively applying substantially constant forces to said pair ofmass members in the direction of the motion of said first mass member asit initiates delivery of impact force to such work element.

2. The percussive tool of claim l in which each of said substantiallyconstant forces is controlled by the respectively associated one of saidpair of means to remain substantially constant during each reciprocatorycycle of said rst mass member and additively to remain approximatelyequal to the average value of such impact force over any operatinginterval comprisinU a continuous sequence of such cycles.

3. In a percussive tool having a casing in which the occurrence ofvibration is undesirable, a hammer reciprocaole within said casing forthe successive intermittent delivery of impact force to animpact-receiving-and-transmitting member, means for reciprocating saidhammer by the application of forces alternately against the respectiveopposite ends thereof whereby reaction forces are alternately developedin opposite directions on said casing tending to vibrate the same, theforce tending to reciprocate said hammer in a direction away from itsimpact relation with such impact-receiving member being in part impactreaction force developed thereagainst during the actual interval ofimpact, a pair of oscillators respectively reciprocable with respect tosaid casing generally along Vthe reciprocatory axis of said hammer,means for reciprocating said oscillators in force opposition to thereciprocatory movement of said hammer whereby counteractive reactionforces are developed that oppose said reaction forces, said oscillatorsbeing dimensioned and arranged so that such counter-active reactionforces approximately equal said reaction forces tending to vibrate thecasing, and a pair of means for supplementing the forces causingreciprocation of said oscillators by respectively applying thereto,generally in the direction of motion of said hammer ima ediately beforethe delivery of impact force thereby to such impact-receiving member,continuous forces operative between said casing and respectiveoscillators and which. additively are substantially equal in averagevalue to the average value of such impact reaction force intermittenlyoperative against said hammer.

4. The percussive tool of claim 3 in which a pair of automatic means areprovided in respective association with said oscillators to enforce suchequality between the average values of said continuous forces and suchimpact reaction force despite variations in the average value of thelatter occurring in any continuous operating interval comprising asubstantial number of impact cycles.

5. The percussive tool of claim 4 in which each of said means providingsaid continuous forces includes means for maintaining the values thereofsubstantially constant during the reciprocatory movement of saidoscillators corresponding to any one reciprocatory cycle of said hammer.

6. The percussive tool of claim 3 in which said oscillators are locatedwith the axes of reciprocation thereof substantially parallel andsymmetrically oriented with respect to the axis of reciprocation of saidhammer.

7. In combination with a percussive tool having a casing containing ahammer reciprocated with a nonconstant frequency by application of areversing force f thereto which simultaneously tends to produce reactivecasing vibration likewise of non-constant frequency, a

pair of oscillatable elements, a support structure for said oscillatableelements, and means for developing a reversing force lbetween saidsupport structure and oscillatable elements for actuating the latter,said support structure tending to vibrate reactively during theoscillatory actuation of said oscillatable elements and being rigidlyrelated with respect to said casing with the axes of movement of saidoscillatable elements being coplanar. and symmetrically related withrespect to the axis of reciprocation of said hammer, said reversingforce developed between said support structure and oscillatable elementsbeing synchronized and quantified with respect to such reversing forcereciprocating said hammer so as to effect a condition of anti-vibrativeforce counterbalance between said casing and said support structure.

8. In a percussive tool, a casing providing a cylinder having endclosures respectively dening upper and lower reaction surfaces, a hammerreciprocable within said cylinder between said reaction surfaces, meansfor applying uid pressure alternately between the respective ends ofsaid hammer and the respectively opposing reaction surfaces toreciprocate said hammer, and a force-counterbalancing system comprisingtwo pairs of opposed counterbalancing surfaces oriented in respectiveopposition to the aforesaid reaction surfaces, a pair of hermeticbarriers respectively interposed between each pair of counterbal- V- theoccurrence of vibration is objectionable and defining a first cylinderand a plurality of second cylinders, a plurality of free pistonsrespectively received within said cylinders for individual oscillatorymotions relative thereto, pneumatic means applying accelerative forcesto each of said free pistons and transmitting corresponding pneumaticreaction forces to said casing, the piston in said rst cylinder being ablow-striking element and the other of said pistons being positionallycontrolled during the oscillatory movement thereof to prevent thetransmission of impact force therefrom to said casing by suitablerelative adjustment of the forces applied to said second pistons, and aplurality of pneumatic feedback means respectively responsive topositions assumed by said second pistons so positionally controlled toaccomplish such adjustment, the algebraic sum of all of the positive andnegative components of said pneumatic reaction forces along the axis ofmotion of said blow-striking piston remaining substantially constantduring the typical oscillatory cycle thereof wherefore vibration of saidcasing along such axis is substantially eliminated.

l0. The pneumatic percussive tool of claim 9 iu which the axes ofreciprocation of said second pistons are substantially parallel and aresymmetrically oriented relative to the axis of reciprocation of saidblow-striking piston and are parallel thereto.

11. The pneumatic percussive tool of claim 10 in which said secondpistons comprise a pair thereof with their axes of reciprocationcoplanar.

12. In a pneumatic percussive tool, a casing in which the occurrence ofvibration is undesirable providing a main cylinder having end closuresrespectively defining upper and lower reaction surfaces, a hammerreciprocable within said main cylinder between said reaction surfaces,an impact-receiving-and-transmitting member slidably carried by saidcasing and extending upwardly into said main cylinder through and insealing relation with a portion of the lower end closure thereof, meansfor applying iluid pressure alternately between the respective ends ofsaid hammer and the respectively opposing reaction surfaces toreciprocate said hammer, a force-counterbalancing system comprising apair of oscillator cylinders provided by said casing and each having endclosures respectively dening upper and lower counterbalancing surfacesoriented in respective opposition to the aforesaid reaction surfaces, apair of oscillators respectively reciprocable within said oscillatorcylinders between the associated counterbalancing surfaces, first tlowconduit means connecting the upper ends of said oscillator cylinderswith the lower end of said main cylinder for simultaneously transferringpressures developed against said lower reaction surface to said uppercounterbalancing surfaces, second flow conduit means connecting thelower ends of said oscillator cylinders with the upper end of said maincylinder for simultaneously transferring pressures developed againstsaid upper reaction surface to said lower counterbalancing surfaces, thearea of each of said reaction surfaces and the aggregate areas of thecounterbalancing surfaces respectively opposed thereby beingapproximately equal, a pair of seal members respectively carried by saidoscillators, a pair of pressurizable enclosures respectively receivingsaid seal members therein and each enclosure being provided with aninlet port adapted to communicate with a source of air under pressureand with an exhaust outlet port, means for establishing within each ofsaid pressurizable enclosures a pneumatic column applying a force to theassociated Seal member, the volume of each of said enclosures being sorelated to the cyclic increases and decreases in the volume of thepneumatic column therein as produced by the cyclic reciprocations of theassociated seal member and oscillator that substantially no change inpressure occurs within the enclosure because of such cyclicreciprocations, each of said seal members being adapted to traverse oneof said ports associated therewith to maintain a selectively variablecontrol over the rate of ow of air through the associated pressurizableenclosure for automatically adjusting the pressure therein to maintainsaid Yoscillators in a condition of impact-preventing separation withthe counterbalancing surfaces respectively associated therewith.

13. The pneumatic percussive tool of claim 12 in which the axes ofrcciprocation of said oscillators are coplanar and symmetrical withrespect to the axis of reciprocation of said hammer.

14. The pneumatic percussive tool of claim 13 in which said axes ofreciprocation of said oscillators are parallel.

l5. The pneumatic percussive tool of claim 12 in which each of said sealmembers is carried by the associated oscillator at the lower endthereof, and in which the associated pneumatic column applies adownwardly oriented force thereagainst.

References Cited in the tile of this patent UNITED STATES PATENTS2,400,650 Leavell et al. May 21, 1946 2,679,826 Leavell June 1, 19542,730,073 Leavell Jan. l0, 1956 2,748,750 Altschuler June 5, 19562,752,889 Leavell July 3, 1956 2,762,341 Solengro Sept. 11, 1956

